CDI-171/CDI-172: Plugin Framework Detection and Execution

[erikostien-pingidentity]

• Add 'protoc' code generation to Makefile, and update some targets for better messaging.
• Update many test cases to initialize koanf when using options.
• Add 'plugin' command for managing PingCLI plugins via Hashicorp's go-plugin module.
  This command includes three subcommands 'add', 'list', and 'remove'.
• Add test cases for new 'plugin' subcommands.
• Remove init() in root.go command in favor of initialization in the NewRootCommand function. This allows the root cobra command instance to initialize plugins if defined.
• Add plugin commands to root command on initialization.
• Update to go 1.24.3 and update various dependencies.
• Update tests to use PingFederate Terraform Provider 1.5.0.
• Update tests to use PingOne Terraform Provider 1.8.0.
• Add Remove() to StringSlice custom type.
• Add PluginError() output type for plugin related system errors.
• Host, connect, and dispense plugins in 'internal/plugins/plugins.go'.
• Use NewKoanfConfig() to initialize main Koanf to avoid odd errors in test cases when run sequentially.
• Protobuf definitions and generated code located in 'internal/proto'
• The 'shared' directory contains all code that a golang-based plugin can use to communicate to the PingCLI host process